M20B25 or B27i

[pw95]

hey guys,

ok so i have a 1989 320i body with a m20b27 motor in. im going to put a turbo in it eventually but i have an issue.

My initial plan was to buy a m20b25 and rebuild it so that i can turbo it and it wouldnt crap out on me, but i did some research and i got mixed reviews about doing a b27i instead of b25. has anyone on here done the b27i build? how does the power compare between the the two (n/a)? and what would i need for the b27i build?

thanks in advance guys,
and keep on keepin' on

[packratbimmer]

One reason to go 2.7 is that you could go with the forged diesel crank. The eta crank is bulletproof, but the forged is even stronger for a turbo set-up. Use the longer rods from the 2.5 and get pistons specifically made for the rod/combustion chamber you choose. There are many sources for custom pistons made for the 885 head and 325i rods out there.

...oh, and more specific questions referencing the research you have done here and there will get you more results here. There is a lot of information on this topic here and E30tech and probably the eta sites.

Cheers

[pw95]

oh awesome ill definitely look into that cheers,

Well some people say the 2.7i makes more power than the 2.5 and others argue that it doesnt, does anyone have real figures on power outputs etc

cheers

[digger]

budget 2.7L dont really make anymore peak power than a b25, but should make more torque. there are several different variants of 2.7i budget builds so it depends

[packratbimmer]

Exactly ^^^

My take on engine builds is:

1) What gear ratios do I want in my transmission and differential? and

2) Do I want low end torque or high end horsepower?

3) Gross weight of car after build + my stuff (tools heavy parts)?

The reason I bring up gear ratios is that it forces a person to figure out where/how they drive or want to drive??? I like to be able to wind out 3rd to 90 on country roads and entrance ramps if I want. I could have a turbo V12 with 4.10 gears and would not be able to go that fast in 3rd.

The cool thing about our cars is that anything is possible....

[modernist]

Regardless of power a budget 2.7 is good fun. Gobs of midrange torque, but as Digger said, power does taper off in the high end.